Duncan, J.M. and Chang, Y.Y. (1970), Nonlinear analysis of stress
and strain in soils, Journal of the Soil Mechanics and Foundation
Division, ASCE, Vo. 96, No. 5.
Wong, K.S and Duncan, JM (1974), Hyperbolic Stress-Strain
Parameters for Nonlinear Finite Element Analysis of Stresses and
Movements in Soil, Department of Civil Engineering, University
of California, Berkeley.